The present invention relates to construction equipment, such as cranes, having an upper works assembly rotatively mounted on a lower works assembly, and more particularly to a method and an apparatus for aligning the upper works to the lower works during redecking of the assemblies.
Construction equipment, such as cranes or excavators, often must be moved from one job site to another. Moving a crane or excavator can be a formidable task when the machine is large and heavy. For example, highway limits on vehicle-axle loads must be observed and overhead obstacles can dictate long, inconvenient routings to a job site.
One solution to improving the mobility of large construction machines is to disassemble them into smaller, more easily handled components. This typically involves undecking (separating) the upper works assembly from the lower works assembly. For larger cranes, further disassembly of the upper works and the lower works may be required. The individual components can then be transported separately to the job site where they are reassembled.
The typical past practice has been to undeck the upper works from the lower works with an outside assist crane. As the upper works assembly for a larger capacity crane may weigh as much as 80,000 lbs., the capacity of the assist crane required represents a very significant transport expense.
As a result, designers have attempted to develop self-handling (self undecking) systems. One such system uses a saddle and counterweights to temporarily support the upper works assembly while the lower works assembly is maneuvered into position underneath the upper works. Another system employs a series of hydraulic jacks that support the upper works assembly during redecking. For examples of previously patented self handling systems, see U.S. Pat. Nos. 4,662,527; 4,632,262; 4,632,261; 4,273,244 and 3,624,784.
The disassembly of a conventional crane can also be both labor-intensive and time-consuming, adding additional expense to the undecking and redecking operations. This is primarily due to the large number of high-strength fasteners connecting the upper works assembly to the lower works assembly.
To overcome this problem, several quick disconnect systems have been developed. Several such machine designs, many of which are patented, are disclosed in an article entitled "Solving The Quick-Disconnect Problem For Big Bearings" in the Jul. 7, 1983 issue of Machine Design. For examples of previously patented approaches to solving this problem, see U.S. Pat. Nos. 4,478,340; 4,436,444; 4,248,488; 3,941,252; 3,923,407; 3,921,817; 3,726,418 and 2,965,245.
Finally, crane redecking can present alignment difficulties as well. In a conventional crane, the bearing bolt holes in the upper works assembly must be aligned precisely with the mounting-surface holes in the lower works assembly during redecking of the crane. Cranes employing quick disconnect systems which undeck at the swing bearing also require precise longitudinal, transverse and vertical alignment.
When redecking is performed with an assist crane, the assist crane operator must maneuver the suspended upper works assembly into transverse and longitudinal alignment with the lower works. When redecking is performed with a self handling system, the driver transporting the lower works assembly must maneuver the lower works underneath and into transverse and longitudinal alignment with the temporarily supported upper works. Because the separate assemblies are large and heavy, such alignments can be unwieldy and time consuming. Uneven terrain can aggravate the problem. Moreover, neither method provides for vertical alignment of the separate assemblies.
One approach to solving the alignment problem for self handling systems is disclosed by U.S. Pat. No. 4,601,401. The patent discloses an alignment system which uses a plurality of centering pins and sockets. As the centering pins engage the sockets, the upper works assembly is forced to translate into alignment.
This system has several disadvantages. First, floats must be provided under each of the jacks supporting the upper works assembly to allow lateral displacement of the upper works during alignment. These floats are expensive and create an inherent instability in the structure during redecking, particularly on uneven terrain. Second, the transport trailer which supports the lower works during redecking is forced to carry the weight of the upper works during alignment. The combined weight of the upper works and the lower works will often exceed the carrying capacity of the transport trailer. Third, after the assemblies have been aligned, the upper works must be raised in order to retract the pins, adding an additional step to the redecking operation. Finally, the system does not provide for vertical alignment of the assemblies.